Definition and general properties
Transition metals are elements whose atoms or ions have an incomplete d-subshell. The first transition series runs from scandium to zinc. They are generally hard, dense, malleable and good electrical conductors.
Characteristic properties
Variable oxidation states arise because 3d and 4s electrons have similar energies. Examples include Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺ and manganese oxidation states from +2 to +7. Their compounds are often coloured, and metal ions form complexes when ligands donate electron pairs, such as [Co(H₂O)₆]²⁺ and [Fe(CN)₆]³⁻.
Catalytic activity
Transition metals provide alternative reaction pathways and can change oxidation state. Examples include MnO₂ in hydrogen peroxide decomposition, iron in the Haber process and V₂O₅ in the Contact process.
Selected reactions
Red-hot iron reacts with steam: 3Fe + 4H₂O → Fe₃O₄ + 4H₂. Copper does not release hydrogen from dilute non-oxidising acids, but oxidising acids such as nitric acid attack it.
Revision table
| Property | Explanation | Example |
|---|---|---|
| Variable oxidation states | Similar d and s electron energies | Fe²⁺/Fe³⁺ |
| Coloured compounds | Electronic transitions involving d orbitals | Cu²⁺ solutions |
| Complex formation | Ligands donate electron pairs | [Fe(CN)₆]³⁻ |
| Catalysis | Alternative pathways | Fe in Haber process |
